RLSA needsLayout on customscrollbar thickness change.

Source/core/rendering/RenderBox.cpp

Index: Source/core/rendering/RenderBox.cpp
diff --git a/Source/core/rendering/RenderBox.cpp b/Source/core/rendering/RenderBox.cpp
index 7e63fe333b7890e7e5c48a84f0ad34a67eb493fb..387f0cda162c9d68dd73fc883a39c22c3d2cfe54 100644
--- a/Source/core/rendering/RenderBox.cpp
+++ b/Source/core/rendering/RenderBox.cpp
@@ -95,6 +95,7 @@ RenderBox::RenderBox(ContainerNode* node)
     , m_intrinsicContentLogicalHeight(-1)
     , m_minPreferredLogicalWidth(-1)
     , m_maxPreferredLogicalWidth(-1)
+    , m_customScrollbarThicknessChanged(false)
 {
     setIsBox();
 }